The objectives of this research project are to synthesize and develop novel targeted nanoglobular gadolinium(III) chelates as safe, effective and tumor-specific contrast agents for diagnostic cancer imaging with magnetic resonance imaging (MRI). The FDA approved clinical MRI contrast agents are nonspecific agents. High doses are often used to achieve accurate cancer diagnosis. However, it has been recently reported that high doses of gadolinium-based contrast agents can cause potentially fatal nephrogenic systemic fibrosis in some patients with renal malfunctions. We believe that an effective tumor specific contrast agent can substantially reduce the injected dose for accurate cancer detection and, therefore, greatly minimize the toxic side effects of gadolinium- based contrast agents. We propose to design, synthesize and evaluate tumor-specific peptide targeted nanoglobular Gd-DO3A conjugates as novel targeted MRI contrast agents for diagnostic cancer imaging. The targeted contrast agents will result in effective tumor specific contrast enhancement at a substantially reduced dose and rapidly eliminate from the body after the MRI examinations. They will significantly improve the safety index of contrast enhanced MRI in cancer diagnosis. The specific aims of the projects are to design, synthesize and characterize tumor-specific peptide targeted nanoglobular Gd-DO3A conjugates from compact and three-dimensional symmetric nanoglobular macromolecules as targeted MRI contrast agents;to evaluate the physicochemical properties, including transmetallation stability and relaxivity, and biological properties, including cytotoxicity, hemotoxicity and tumor binding of the targeted nanoglobular MRI contrast agents;to investigate the efficacy of the targeted nanoglobular contrast agents for tumor-specific contrast enhanced MR imaging in animal tumor models at reduced doses; to evaluate in vivo toxicological and pharmaceutical properties, including acute and subacute toxicity, pharmacokinetics, elimination, Gd tissue accumulation and tumor targeting of the targeted nanoglobular MRI contrast agents. The long-term goal is to develop safe, effective and targeted MRI contrast agents for specific cancer imaging. Novel tumor-specific MRI contrast agents will be designed and developed for more accurate and earlier cancer detection. Accurate cancer diagnosis will be achieved with the targeted contrast agents at a substantially reduced dose, which will further improve the safety of contrast enhanced MRI.